When driving a vehicle on rough roads or in off-road conditions, terrain features presenting a relatively abrupt change in gradient of the driving surface may be encountered. For example, steep downward gradients may be encountered abruptly as a vehicle negotiates terrain features such as pot-holes, craters, trenches, steps or the like. When such a terrain feature is encountered, the vehicle may experience relatively abrupt acceleration as one or both leading wheels begin to descend the gradient. The increase in acceleration may be followed by an abrupt deceleration when the vehicle completes travel over the downward gradient. In the case of a pot-hole, trench or the like the vehicle may then abruptly encounter a relatively steep upward gradient which it may be necessary to negotiate in order to exit the terrain feature. Encountering such terrain features can adversely affect composure of the vehicle and bring discomfort to an occupant.
It is known to provide a vehicle speed control system, such systems typically being referred to as cruise control systems. In such systems vehicle speed is maintained once set by the user without further intervention by the user so as to improve the driving experience for the user.
The user selects a speed at which the vehicle is to be maintained, and the vehicle is maintained at that speed for as long as the user does not apply a brake or, in some systems, the clutch. The cruise control system takes its speed signal from the driveshaft or wheel speed sensors. When the brake or the clutch is depressed, the cruise control system is disabled so that the user can change the vehicle speed without resistance from the system. If the user depresses the accelerator pedal the vehicle speed will increase, but once the user removes his foot from the accelerator pedal the vehicle reverts to the pre-set cruise speed.
More sophisticated cruise control systems are integrated into the engine management system and may include an adaptive functionality which takes into account the distance to the vehicle in front using a radar-based system. For example, the vehicle may be provided with a forward-looking radar detection system so that the speed and distance of the vehicle in front is detected and a safe following speed and distance is maintained automatically without the need for user input. If the lead vehicle slows down, or another object is detected by the radar detection system, the system sends a signal to the engine or the braking system to slow the vehicle down accordingly.
Such systems are usually operable only above a certain speed, typically around 15 mph, and are ideal in circumstances in which the vehicle is travelling in steady traffic conditions, and particularly on highways or motorways. In congested traffic conditions, however, where vehicle speed tends to vary widely, cruise control systems are ineffective, and especially where the systems are inoperable because of a minimum speed requirement. A minimum speed requirement is often imposed on cruise control systems so as to reduce the likelihood of low speed collision, for example when parking. Such systems are therefore ineffective in certain driving conditions (e.g. low speed) and are set to be automatically disabled in circumstances in which a user may not consider it to be desirable to do so.
It is also known to provide a control system for a motor vehicle for controlling one or more vehicle subsystems. U.S. Pat. No. 7,349,778, the content of which is hereby incorporated by reference, discloses a vehicle control system comprising a plurality of subsystem controllers including an engine management system, a transmission controller, a steering controller, a brakes controller and a suspension controller. The subsystem controllers are each operable in a plurality of subsystem function modes. The subsystem controllers are connected to a vehicle mode controller which controls the subsystem controllers to assume a required function mode so as to provide a number of driving modes for the vehicle. Each of the driving modes corresponds to a particular driving condition or set of driving conditions, and in each mode each of the sub-systems is set to the function mode most appropriate to those conditions. Such conditions are linked to types of terrain over which the vehicle may be driven such as grass/gravel/snow, mud and ruts, rock crawl, sand and a highway mode known as ‘special programs off’ (SPO). The vehicle mode controller may be referred to as a Terrain Response® (TR) System or controller.